1. Field of the Invention
The present invention relates to a resin sealed semiconductor device, more particularly, to a resin sealed semiconductor device used for such devices as lighting system devices for vehicles.
2. Description of the Related Arts
FIG. 9 is a schematic plan view of a conventional resin sealed semiconductor device. FIG. 10 is a transparent perspective diagram thereof. Referring to these figures, onto a lead frame 1 are mounted a semiconductor element and a controlling semiconductor element 3, which element 3 is an integrated circuit for controlling the semiconductor element 2. The lead frame 1 is, for example, nickel plated onto a copper base material. In addition, between leads 1a and 1b is a ceramic chip resistance 15, which is a current-detecting resistance, fixed by solder 20, as shown in FIG. 11. The ceramic chip resistance 15 has, for example, silver, palladium and other conductor electrodes on the surface of an alumina plate. The emitter electrode 14 of the semiconductor element 2, the controlling semiconductor element 3 and the ceramic chip resistance 15, are electrically connected by means of the lead 1a.
The semiconductor element 2 has its base electrode 16 electrically connected to an external input electrode 10 by means of a lead 1c. The front end of leads 1d, 1b, and 1c serve respectively as an external output electrode 8, an external ground electrode 9, and an external input electrode 10, and are connected to an external circuit which is not illustrated. The emitter electrode 14 of the semiconductor element 2 is electrically connected to the lead 1a by a thin metallic wire 5 such as an aluminum wire, while the controlling semiconductor element 3 is electrically connected to the leads 1a, 1b, 1c, and the like by thin metallic wires 6 such as gold wire. As illustrated in FIG. 9, the semiconductor element 2, the lead frame 1, and the like are encapsulated with a molded resin 7, excluding the external output electrode 8, external ground electrode 9, and external input electrode 10. In FIG. 8, the molded resin 7 is not illustrated.
The conventional resin sealed semiconductor devices have the above-described structure. An equivalent circuit of the resin sealed semiconductor device shown in FIG. 9 is illustrated in FIG. 12. Referring to the figure, a pulse signal is input from an external circuit (not shown) to the external input electrode, and the semiconductor element 2 is driven. At this time, when the pulse input signal is in a high state, current which flows in the ceramic chip resistance 15 is detected, so that current in excess of a predetermined amount does not flow in the semiconductor 2. The controlling semiconductor device 3 operates to control the current which flows in the semiconductor element 2 at a constant level.
As described above, in the resin sealed semiconductor device, the ceramic chip resistance 15 has been soldered to the leads 1a and 1b. This has given rise to problems such as variations in resistance values depending on the amount of solder used, and changes in resistance values caused by fatigue of the solder across the ceramic chip resistance 15 when an endurance test was carried out for a long period of time. There have been additional problems such as large differences in the coefficient of thermal expansion between the ceramic chip resistance 15 and the leads 1a and 1b, and the apparatus's weakness to heat stress, producing, during operation, deformations which crack the solder. Further, when the ceramic chip resistance 15 had a low resistance, for example 30 m.OMEGA., its precision dropped, reducing yield and increasing costs.